HS748 Taxispeed

[rlepage]

As I saw mentioned in a previous post taxi-ing the 748 is far to sensitive.
It is virtually impossible to taxi at a steady speed without keeping tapping the brakes.It just rockets off as soon as you increase the throttles.
I found a solution.Open the aircraft file and scroll down to the propeller entry ,delete all the entries beneath upto but not including "reference speeds"
then add the following entries in its place
[propeller]
propeller_type= 0
propeller_diameter= 10.000
propeller_blades= 4
propeller_moi= 120.000
beta_max= 86.000
beta_min= 10.000
min_gov_rpm= 4500.000
prop_tc= 0.004
gear_reduction_ratio= 7.600
fixed_pitch_beta= 0.000
low_speed_theory_limit= 80.000
prop_sync_available= 1
prop_deice_available= 1
prop_feathering_available= 1
prop_auto_feathering_available= 1
min_rpm_for_feather= 700.000
beta_feather= 86.000
power_absorbed_cf= 0.900
defeathering_accumulators_available= 1
prop_reverse_available= 0
minimum_on_ground_beta= 0.000
minimum_reverse_beta= 0.000

these values are taken from the viscount 800 which doesnt have problems with overspeed when taxying and seem to fix the taxy problems in the 748,
not sure how it will affect the flight characturistics but i took it for a quick circuit and seemed to be ok.Will do further testing tomorrow.
I have no Idea what all these values mean and im sure it affects how the aircraft flies and will probably now fly like an underpowered viscount but it seemed to do the trick.
Please remember to backup the original aircraft file first and if it doesn't work just move the backup to the 748 folder and ovewrite the one you have edited.
Please feel free to comment.

Regards

Richard

[DaveB]

Hi Richard

Thanks for your input

Two things however..
1. The 748 probably should feel like an underpowered Viscount as it has 2 engines less
and
2. The Viscount has gust locks which 'tame' the old girl a little on the ground.

I don't think it's possible to 'hands off' taxi any of our turbo props without an impact on flight performance due to the nature/short comings of the FS turbo-prop model. Piston props aren't bad and pure jets aren't bad but a mixture of the 2 gets lost in the mud somewhere and this is the same for most if not all FS turbo-props. Granted, the 748 isn't as easy as some to taxi but to be honest.. it's easy enough to work around if you're paying attention.. which you should be

ATB

DaveB

[Garry Russell]

In real life all the Dart aircraft used quite a highpower setting to move off then throttled right back once moving.

I do that with the models and have little trouble

[Motormouse]

In real life all the Dart aircraft used quite a highpower setting to move off then throttled right back once moving.

I do that with the models and have little trouble

Thats' correct, been there, done that (Fokker 27!) use your ears, when the prop just starts to 'pitch' you get a distinctive
change in engine note (@10,600 rpm IIRC), once moving back to ground fine and watch the t's and p's

ttfn

Pete

[rlepage]

Yes thats the theory behind it, unfortunately as has been previously stated FS doesnt model taxying turboprops very well.
You have to get the setting spot on or you will either rocket off or come to a stop.
Done some further testing with these values and doesnt seem to affect the flight model too bad.
Maybe slightly overpowered on takeoff and slightly higher cruise speed than the original.
Just need slightly lower thrust to maintain optimum cruise speed,I can live with that.

Regards

Richard

[TSR2]

Horses for courses, but I'd rather have an acurate flying model than one that doesn't require so many dabs on the brake.

[johnhinson]

As I saw mentioned in a previous post taxi-ing the 748 is far to sensitive.
It is virtually impossible to taxi at a steady speed without keeping tapping the brakes.It just rockets off as soon as you increase the throttles.
I found a solution.Open the aircraft file and scroll down to the propeller entry ,delete all the entries beneath upto but not including "reference speeds"
then add the following entries in its place
[snip]
Regards

Richard

Thanks, Richard, I will certainly try that. It was me that touched on the subject in the thread "we are blessed", which caused that discussion to unfortunately go off course because what started as a side-comment rather took things over! I'm pleased you have started a separate thread.

Whilst I respect Ben's comments about having the flight characteristics right, it might be possible to adjust down any excess power having got the taxying more controllable as described.

Incidentally, reference the Viscount, not too long ago I downloaded some updated FDEs but found these displayed similar taxying characteristics (so reverted back out of choice) so I guess perfection is always going to be something of a juggling act.

Best wishes,

John

[Garry Russell]

Depends what you call excessive speed

The normal taxy speed for a Viscount was 35-40MPH. In the real world, crews would set the throttle and use the brake to control speed if it go too quick as it was easier than adjusting the throttle

As I mentioned above I don't get a problem with opening up then throttling back.

In all honesty I think this is a solution to a problem that does not really exist...not to any great extent anyway.

The real problem is VA clients making silly rules like low taxy speeds giving a false impression and folks not using the correct throttle settings and techniques.

The Viscount for example should be taxyied on two engines with the outers throttled right back on outbound and shut down after landing.

Believe me, a lot of time is spent on setting these models up to fly right and handle correctly on the ground with the best compromise if needed.

[Viscount Cornbank]

The flight manuals actually state that the throttles should be opened up to 10500-11000 rpm (just on the periphery of the constant speeding range, when the blades start making farting noises) to get the aircraft moving and thereafter control the speed with the brakes. Indeed on Dart 6 engines the range between idle at around 7500 rpm and up to 9500rpm is prohibited.

cheers

Fraser

[johnhinson]

Absolutely, I don't dispute the right way to taxi and fly the things but we don't all have state of the art controls and I experience exactly the same as has been described - you open up power, the aircraft rockets off unrealistically, you shut back power and it grinds to a halt unrealistically. So yes, I try to control by brake but then the forward view bobs up and down like a grasshopper because I don't have pedals to apply anything between brake off/brake on - I wouldn't like to be a passenger enduring that.

So please, chaps, don't be so heavily defensive but give us some understanding that what works for you won't work for everybody's setup. We aren't trying to rubbish the model or its characteristics, just trying to get some better pleasure from using it on our own systems.

John